The present invention relates to ablation methods and apparatus, e.g., such as those used for cardiac therapy. More particularly, the present invention pertains to apparatus and methods that use monitoring of acoustic energy to control and/or provide information regarding ablation processes.
Catheters for electromagnetic ablation are known and are commonly used to treat various diseases and medical disorders. Typically, the catheter includes an energy-delivering electrode that is coupled to a source of electromagnetic energy, e.g., an electrosurgical generator. Other electrodes can be proximally positioned on the catheter and can be used for sensing and other related electrical purposes. The generator energizes the electrode, which then transfers the energy to tissue disposed adjacent thereto. The surgical energy is typically applied to the tissue at a selected level and for a selected duration to effect a biological change in the tissue.
In prior procedures, the ablation catheter is employed to alter tissue. In order to ablate the tissue, electromagnetic energy is applied to create a lesion via the energy-delivering electrode without regard to the specific level of electromagnetic energy supplied by the generator. In situations where too much electromagnetic energy is delivered to the tissue during the electrosurgical procedure, the tissue xe2x80x9cpops,xe2x80x9d thus indicating the application of an excessive amount of energy.
As such, when the ablation electrode has firm contact with tissue and high power is applied, an undesirable crater may be formed at the contact site. When crater formation occurs, electromagnetic energy directed by the ablation electrode causes cells within the tissue to explode, thus creating the popping sound that may even be heard outside the patient""s body. Crater formation may cause an uncontrolled high-volume lesion. To further patient safety, prevention of crater formation is desired because it is unknown how much of an effect crater formation has on the occurrence of thromboembolic incidents.
In other words, high-strength electromagnetic energy can cause tissue cells to be undesirably destroyed during certain medical procedures, e.g., ablation. As such, the delivery of such energy needs to be effectively controlled.
Further, electrosurgery cutters and ablation catheters use such electromagnetic energy. While a cut with an electrosurgical cutter is very deep and performed relatively fast, an ablation lesion formed by an ablation catheter should be precise. In other words, lesion size should also be controlled, and at least one way to control lesion size is to control the delivery of the energy to the ablation site.
Therefore, for at least the above reasons, some ablation systems known in the art include sophisticated power control systems. Such control systems use various techniques to monitor the ablation process and control the delivery of energy to the desired ablation site.
For example, catheters including temperature measurement sensors allow for control of an ablation energy generator such that an appropriate constant temperature of the ablation electrode can be maintained. However, when the temperature is low, the lesion may not be sufficient to effectively destroy the tissue. If the temperature rises too high, e.g., above 70 degrees Celsius, coagulation on the electrode may occur and undesirably increase the impedance of the ablation system.
Further, for example, U.S. Pat. No. 5,733,281 to Nardella entitled xe2x80x9cUltrasound and Impedance Feedback System for Use with Electrosurgical Instruments,xe2x80x9d issued Mar. 31, 1998, discloses an electrosurgical feedback system that includes an acoustical detection element and/or an impedance determination circuit. The acoustical detection element may include an ultrasonic transducer that acoustically detects the effects of energy on tissue, such as the generation of steam created during the heating process. The acoustical detection element generates an acoustic output signal that may regulate the application of power to an energy delivering electrode. Nardella further discloses that the acoustical detection element may include a microphone coupled to a speaker for producing an audible output signal.
Various other problems may also be present in an ablation process. For example, to use the maximal amount of ablation energy, the energy-delivering electrode preferably should have an intimate contact with the cardiac tissue. Because of cardiac contractions, dislodgement of the electrode from the desired position may occur.
Electrophysiologists usually monitor intracardiac potentials to confirm the proper position (e.g., stability of) as well as the proper contact of the electrode with tissue, e.g., the endocardium. However, the intracardiac potential is discontinuous, being characterized with intrinsic deflection that is repetitive at the frequency of heart beats. Distinct ST wave amplitude elevation caused by the injury current may be used to confirm the pressure of the electrode to the cardiac muscle. However, dislodgement may also occur anywhere within the cardiac cycle while there is no intracardiac signal.
Table 1 below lists U.S. Patents relating to various ablation techniques.
All documents listed in Table 1 above, and further elsewhere herein, are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments, and claims set forth below, many of the devices and methods disclosed in the documents of Table 1 and other documents incorporated by reference herein may be modified advantageously by using the teachings of the present invention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the art with respect to ablation of tissue. One such problem involves the inadvertent creation of an ablation crater. Another problem involves lack of stability of an ablation catheter during ablation due to physiological events, e.g., heart contractions.
In comparison to known ablation techniques, various embodiments of the present invention may provide certain advantages. For example, the present invention provides apparatus and methods that enable a practitioner to acoustically monitor ablation of tissue and control the amount of electromagnetic energy directed to the tissue to prevent crater formation. Further, the present invention provides systems and methods that increase stability of an ablation catheter during ablation by acoustically monitoring ablation and indicating instability to the practitioner. Further, the present invention provides systems and methods for monitoring both acoustical energy and temperature during ablation to aid in preventing crater formation.
Some embodiments of the present invention may provide one or more of the following features for ablating tissue: providing a catheter including an ablation electrode; ablating tissue using an ablation electrode, wherein the ablation electrode directs electromagnetic energy to the tissue; detecting at least acoustical energy resulting from ablation of tissue (e.g., cardiac tissue); comparing detected acoustical energy to at least a portion of an ECG waveform to determine stability of a catheter; determining whether detected acoustical energy is synchronized with at least a portion of an ECG waveform; controlling electromagnetic energy directed to tissue based on comparing detected acoustical energy to at least a portion of an ECG waveform; detecting at least acoustical energy resulting from ablation of tissue using a piezoelectric transducer element; detecting an ablation temperature using a piezoelectric transducer element; controlling electromagnetic energy directed to tissue based on a detected ablation temperature; simultaneously controlling electromagnetic energy directed to tissue based on detected acoustical energy and detected ablation temperature; analyzing detected acoustical energy to detect at least one popping sound; reducing electromagnetic energy directed to tissue if at least one popping sound is detected; removing at least a cardiac generated acoustical energy component from a transducer signal; controlling electromagnetic energy directed to tissue based on a transducer signal having at least a cardiac generated acoustical energy component removed therefrom; comparing a transducer signal to a predetermined popping sound spectrum to determine the presence of a popping sound; reducing electromagnetic energy directed to tissue if a transducer signal and at least a portion of an ECG waveform are asynchronous; and triggering an electrode stability alarm if a transducer signal and at least a portion of an ECG waveform are synchronous.
Some embodiments of the present invention may provide one or more of the following additional features for ablating tissue: providing a catheter including an ablation electrode and a tensiometric element; detecting a plurality of cardiac contractions using a tensiometric element and providing a tensiometric signal representative of a plurality of cardiac contractions; controlling electromagnetic energy directed to cardiac tissue based on a compared tensiometric signal and transducer signal; and detecting acoustical energy, wherein the detected acoustical energy includes a plurality of sound events, wherein comparing a tensiometric signal to a transducer signal includes measuring a time interval between at least one sound event and at least one cardiac contraction.
Further, some embodiments of the present invention include one or more of the following features for an ablation apparatus: a catheter body; an ablation electrode proximate a distal end of a catheter body, wherein the ablation electrode is operable to direct electromagnetic energy to tissue; a piezoelectric transducer element proximate a distal end of a catheter body, wherein the piezoelectric transducer element is operable to detect acoustical energy and temperature and provide a transducer signal representative of detected acoustical energy and temperature; an ablation electrode that includes a ring electrode including an outer radial surface and an inner radial surface, wherein the inner radial surface defines an inner volume, wherein a piezoelectric transducer element is located proximate the inner volume of the ablation electrode, and further wherein the piezoelectric transducer element is acoustically coupled to the inner radial surface of the ablation electrode; a piezoelectric transducer element that includes a piezoelectric film having an inner radial surface and an outer radial surface, wherein the outer radial surface of the piezoelectric film is acoustically coupled to the inner radial surface of an ablation electrode by a conductive adhesive layer; a detection sensor operable to detect acoustical energy; controller circuitry in communication with sensing circuitry and a detection sensor, wherein the controller circuitry is operable to compare detected acoustical energy to an electrocardiogram to determine stability of a catheter when the catheter is positioned for performing an ablation process; and controller circuitry operable to control electromagnetic energy directed by an ablation electrode to tissue based on detected acoustical energy and an electrocardiogram.
Some embodiments of the present invention include one or more of the following additional features for an ablation apparatus: a detection sensor including a piezoelectric transducer element; a catheter that includes a catheter body, wherein a piezoelectric transducer element is positioned proximate an ablation electrode of the catheter; controller circuitry operable to remove at least a cardiac generated acoustical energy component from a transducer signal and to detect at least one popping sound based on the transducer signal having the at least a cardiac generated acoustical energy component removed therefrom; controller circuitry operable to compare a transducer signal to an acoustic profile representative of a popping sound and reduce electromagnetic energy directed to tissue if the transducer signal includes at least one popping sound; controller circuitry operable to simultaneously control electromagnetic energy directed to tissue based on detected acoustical energy and detected ablation temperature; controller circuitry operable to detect at least one popping sound based on a comparison between a transducer signal having at least a cardiac generated acoustical energy component removed therefrom and an acoustic profile representative of a popping sound; controller circuitry operable to measure a sound intensity of detected acoustical energy based on a transducer signal; controller circuitry operable to compare a transducer signal to at least a portion of an ECG waveform signal if a measured sound intensity is greater than a sound intensity threshold; is controller circuitry operable to reduce electromagnetic energy directed to tissue if a transducer signal and at least a portion of an ECG waveform signal are asynchronous; and controller circuitry operable to trigger an electrode stability alarm if a transducer signal and at least a portion of an ECG waveform signal are synchronous.
Some embodiments of the present invention include one or more of the following additional features for an ablation apparatus: a catheter including an elongated catheter body, an ablation electrode proximate at a distal end thereof, and a tensiometric element lying along a length of the catheter body, wherein the ablation electrode is operable to direct electromagnetic energy to cardiac tissue, and further wherein the tensiometric element is operable to provide a tensiometric signal representative of a plurality of cardiac contractions; controller circuitry operable to compare a tensiometric signal to a transducer signal; controller circuitry operable to control electromagnetic energy directed to cardiac tissue based on a comparison between a tensiometric signal and a transducer element; and controller circuitry operable to measure a time interval between at least one cardiac contraction and at least one sound event of a plurality of sound events of detected acoustical energy.
The above summary of the invention is not intended to describe each embodiment or every implementation of the present invention. Rather, a more complete understanding of the invention will become apparent and appreciated by reference to the following detailed description and claims in view of the accompanying drawings.